Abstract

Recent advances in Doppler techniques have enabled high sensitivity imaging of biological flow to measure blood velocities and vascular perfusion. Here we compare spectrometer-based and wavelength-swept Doppler OCT implementations theoretically and experimentally, characterizing the lower and upper observable velocity limits in each configuration. We specifically characterize the washout limit for Doppler OCT, the velocity at which signal degradation results in loss of flow information, which is valid for both quantitative and qualitative flow imaging techniques. We also clearly differentiate the washout effect from the separate phenomenon of phase wrapping. We demonstrate that the maximum detectable Doppler velocity is determined by the fringe washout limit and not phase wrapping. Both theory and experimental results from phantom flow data and retinal blood flow data demonstrate the superiority of the swept-source technique for imaging vessels with high flow rates.

Figures (5)

Theoretical predictions for velocity limitations of swept-source and spectrometer-based Doppler OCT systems. The minimum velocity and wrapping velocity are the same for both systems. The spectrometer-based washout velocity equals the wrapping velocity, but the washout limit is several orders of magnitude greater for the swept-source system.

Retinal data acquired from the optic nerve region of the left eye in the same subject using a commercial SDOCT system (A-C) and the custom swept-source system (D-F). (A) Retinal SVP image consisting of 512x200 lines from the SDOCT system. Dashed lines labeled b and c indicate positions of cross-sectional images in (B) and (C). (D) SVP image consisting of 256x200 lines from the swept-source system. Dashed lines labeled e and f indicate positions of cross-sectional images in (E) and (F). Yellow arrows indicate regions of washout caused by high blood flow. Fringe washout artifacts are present in the commercial SDOCT data. The swept-source data is free from washout artifacts allowing for flow detection in the indicated vessels.

Axial shift correction of SSOCT Doppler image by velocity interpolation. (A) Original Doppler B-scan image of the flow phantom at the highest tested speeds after phase unwrapping. (B) Corrected Doppler image using velocity interpolation. (C) Velocity profiles taken from (A) and (B) along the dashed line. The axial shift artifact does not contribute significantly to the image as seen by the close correlation of the original and corrected profiles.